Electric discharge lamp



July 28, 1953 T. E. FOULKE ELECTRIC DISCHARGE LAMP Filed NOV. 29, 1951 Inventor: Ted EpFoulKe. yMK-K His Attor ey Patentecl July 28, 1953 to General Electric :Com

New York pane a corporation of AppIicationNnveiriber 219, '1951,'Serial No.2 58,911

5 Claims. I

By invention relates to gaseous electric dis- .charge lamps generally, and more .panticulafly to ultraviolet .lamps of the negative glow ty e. .Still more particularly, my invention relates'to negar tive glow lamps .of the type employing .a gas ,fllling comprising nitrogen as a source .of ultraviolet radiations.

It is an object .of my invention .to improve the performance of such lamps in respect to such factors as .high ultraviolet "light .emissionfor along useful life. ,It is a further-object to obtain high ultraviolet emission and long useful life Without adversely afiecting the breakdown and operating voltage characteristics or" .Slif-lh lamps- Ultravio'let glow lamps as hcrlitbiore tuted have employed .a filling consisting DI argon with to per cent of nitrogen. Elli life of such lamps has been 11311116121 flu? 1 .0 ".gflfiain p f h nitro en- In fact, .attenm stoimafn certain small types of such lamps have proved futile because the nitrogen was entirely cleaned up during activation of the electrodes, presumably by combination of the nitrogen with the activating alkaline earth metals usually employed on the electrodes. or an increase in the nitrogen content resulted in lamps having a high breakdownand operating voltage, and also resulted in uncertainlocation and stability of'the corona discharge.

In accordance with the present inventionji have found that the di-fiiculties referred to ,a'bov'e are eliminated by theaddition to thegas filling of a substantial proportion of helium. It seems that with .over .5 13.81 cent of helium and a few per cent of nitrogen in a mixture of argon, helium and nitrogen, the nitrogen *is not rapidly "cleaned up, but is retained for .an appreciable :time in the gas phase by the presence of the helium, 1121-.- proved results may be obtained by employing the three-,components of the gas filling in :a "wide range, by volume, of 5 to 80 percent helium, .5 to 15 per cent nitrogen, and the balance argon. For the best maintenance of ultraviolet 'outputat the lowest voltage I prefer a range of 5 to 15 per cent nitrogen, 15 to per cent helium and the balance argon. With one type of lamp containing an optimum composition of 65 per cent argon, 25 per cent helium and 10 per cent nitrogen, I have obtained a useful ultraviolet output for a life three times as long as that obtained with otherwise similar lamps containing, at the same pressure, the argon-nitrogen mixture with no helium. In the case of certain other very small lamps, wherein the results were entirely negative when employing the argon-nitrogen mixture be- The use of higher pressures 1 cause of clean .up ,of nitrogen, -I :have obtained a useful life ,excess .of 100 hours 'by the addition of helium.

I have found, in general, that the hi her content of helium in the mixture gives higher absolute ultraviolet .output 1181 of current, although the breakdown voltage .of the lamp iises. .While the increased voltage may limit the use .bflhigher helium cem nts in lamps operating on .eommercial circuits ghav'inga fixed voltage, such as the conventional 1054125 volt circuits. the increased ultraviolet output may "he availed of in special circuits. For operation at lowest voltage together with good ultraviolet maintenance, 11 prefer to employ a content of 'heliumgrea'ter than about 15;per.cent but less than ab ut 35 per cent. .1 also prefer to employ the three-component gas filling at a total pres ure in the ran of about 10 to 25 mms. 'l-Ig at room'temperature Kabout .fil). E). v l

iurther understan in of inventi n re enenee-mavhehad t th a companying d awtvhe ein Fi s. ;1 and '2 are elevations sh win by way of exampl two Iormsof glow l mps in which the .gas filling composition comprising my invention may be employed.

" Referring to Fig. ..l., the lamp shown the in comprises .a bulb or envelope 1 of glass which is ,perm.eab1e t the ultravio t "r diations (mainly about 3230-3800 angstroms") emittediby the discharge therein- Th ulb ntains apair ofectiuated cold electrodes "2 of'the soecalled fsplit acorn' type and which are supported by a pair vVQflead-inwires13 which are sealed througha conventional glass stem tube t sealed to'the end of the bulb I; The electrodes '2 mayc-onsistof sheet nickel of generally one-quarter hemispherical shape and they are activated with a coating 5 of electron emitting material, preferably alkaline "earth "materials such as barium and strontium carbonates which are 'fbrcken down, in known manner, to-form the corresponding oxides. The inner surfaces of theelectrodes 2 are preferably coated in known manner with an alumierat'e at an energy consumption of about 2; Watt with a current of 2 milliamperes. The following table illustrates the life performance of such lamps containing various proportions of the argon-helium-nitrogen filling, and the relative ultraviolet output (UV) and alternating-current breakdown-voltage (BD) obtained thereby.

discharge lamp comprising a sealed light-transmitting envelope having electrodes sealed therein and spaced relatively closely for a glow discharge therebetween and containing a fixed gas 5 filling consisting of substantial proportions of argon, nitrogen and helium at a total pressure in the range of about -25 mm., the nitrogen Percent 0 Hrs. 120 Hrs, 528 Hrs. 792 Hrs. 1,228 Hrs.

Ar He N2 UV BD UV BD Uv BD UV BD UV BD 85 o 34 so s3 s3 54 82 77 10 13.1 78 so s4 s4 82 79 v 66 e7 69 19. s 11. 3 71 s9 76 '88 st so 83 91 59 61 29. 6 9. 4 83 as 77 81 so 77 75 95 as 95 53 39. 2 7. s 106 84 ss 89 97 89 104 105 35.3 80.0 3.5 95 87 so 97 84 as 77 11o The optimum composition of 65 per cent argo 9O constituting, by volume, about 5 to 15 per cent per cent helium andlO per cent nitrogen resulated in a useful ultraviolet output, to the same degree of depreciation, for a period approximately three times as long as with otherwise similar lamps containing only the two-component gas mixture of argon and nitrogen.

The lamp shown in Fig. 2 comprises a tubular glass bulb I of small size, for example approximately /4 inch diameter, and an over-all length of about 11% inches. The bulb 1 contains a pair of electrodes 8, of nickel wire, for example, which are mounted on lead-in wires 9 extending through a flattened press portion 10 at the end of the bulb 1. The electrodes 8 may be activated with a coating ll of alkaline earth materialsas described in connection with the lamp of Fig. 1. Such lamps are designed to operate at an energy consumption of about #25 watt from a source of 105-125 volts at a current of .3 milliampere.

It is virtually impossible to make such lamps with the usual gas filling of argon and nitrogen due to cleaning up of the nitrogen. However, by employing the three-component gas mixture of argon, helium and nitrogen in accordance with my invention such lamps are operable for a useful life in excess of 100 hours. With the optimum gas filling of per cent argon, 10 per cent nitrogen and 25 per cent helium, at a pressure of about 15 mms. at room temperatures, such lamps start at about volts on an alternating current source and at about 98 volts on a direct current source.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An ultraviolet-emitting gaseous electric glow discharge lamp comprising a sealed light-transmitting envelope having electrodes sealed therein and spaced relatively closely for a glow discharge therebetween and containing a fixed gas filling consisting of substantial proportions of 6 argon, nitrogen and helium at a total pressure in the range of about 10-25 mm.

2. An ultraviolet-emitting gaseous electric glow of the mixture and the helium being greater than 5 per cent of the total.

3. An ultraviolet-emitting gaseous electric glow discharge lamp comprising a sealed light-transmitting envelope having electrodes sealed therein and spaced relatively closely for a glow discharge therebetween and containing a fixed gas filling consisting of substantial proportions of argon, nitrogen and helium at a total pressure in the range of about 10-25 mm., the nitrogen constituting, by volume, about 5 to 15 per cent of the mixture and the helium between 5 and percent with the remainder argon.

4. An ultraviolet-emitting gaseous electric glow discharge lamp comprising a sealed light-transmitting envelope having electrodes sealed therein and spaced relatively closely for a glow discharge therebetween and containing a fixed gas filling consisting of argon, nitrogen and helium at a total pressure in the range of about 10-25 mm. and in proportions, by volume, in the range of about 5 to 15 per cent nitrogen, 15 to 35 per cent helium and the balance argon.

5. An ultraviolet-emitting gaseous electric glow discharge lamp comprising a sealed light-transmitting envelope having electrodes sealed therein and spaced relatively closely for a glow discharge therebetween and containing a fixed gas filling consisting of argon, nitrogen and helium at a total pressure in the range of about 10-25 mm. and in proportions, by volume, of approximately 65 per cent argon, 25 per cent helium and 10 per cent nitrogen.

TED E. FOULKE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name I Date 0 1,954,958 Smythe Apr. 17, 1934 1,965,587 Foulke July 10, 1934 2,228,327 Spanner Jan. 14, 1941 2,515,699 Davidson July 18, 1950 

1. AN ULTRAVIOLET-EMITTING GASEOUS ELECTRIC GLOW DISCHARGE LAMP COMPRISING A SEALED LIGHT-TRANSMITTING ENVELOPE HAVING ELECTRODES SEALED THERE- 